This invention relates to a method for the production of a porous cross-linked polymer which carries out continuously the component steps thereof ranging from a step of supplying a water-in-oil type high internal phase emulsion (hereinafter referred to briefly as xe2x80x9cHIPExe2x80x9d) through the step of performing polymerization thereof in the production of the porous cross-linked polymer, preferably a porous cross-linked polymer having continuous cells having communicating pores formed in the surface and the interior thereof (hereinafter referred to also as xe2x80x9copen cellsxe2x80x9d) by the polymerization of HIPE. More particularly, this invention relates to a method for the production of a porous cross-linked polymer which carries out continuously the component steps thereof ranging from a step of supplying the HIPE through a step of polymerizing the HIPE, and can be widely applied to (1) liquid absorbent materials such as, for example, {circle around (1)} core materials in disposable diapers to be used for absorbing water and excrements including urine; and {circle around (2)} agents for disposing of a waste oil and agents for disposing a waste solvent to be used for absorbing oils and organic solvents; (2) energy absorbent materials such as, for example, sound insulating materials and heat insulators in automobiles and buildings to be used for absorbing sound and heat; and (3) chemical impregnating substrates such as, for example, products of toiletry goods impregnated within aromatic agent, a detergent, a lustering agent, a surface protecting agent, and a flame-retarding agent. Further, this invention aims at providing a method for the production of a porous cross-linked polymer which, by selecting the quality of the material for the part destined to be exposed to the HIPE during the course of polymerization, is endowed with a structure having continuous cells (open cells) having communicating pores formed in the surface and the interior of the porous cross-linked polymer, has an improved liquid-passing speed, a liquid-absorbing ratio, and a liquid-absorbing capacity, and is awarded ample freedom in the selection of the composition of HIPE, the device for polymerization, and the conditions of polymerization.
Methods for producing a porous cross-linked polymer by polymerizing the HIPE are disclosed in WO-A-97-27240 and WO-A-97-37745, for example.
WO-A-97-27240 discloses as a method for producing a porous cross-linked polymer by the polymerization of the HIPE through the medium of a film a method for the combined continuous-batch polymerization which comprises continuously filling the HIPE in a vertical (perpendicular) ribbon-like zippered bag of resinous film, reeling the filled bag, and polymerizing the HIPE in the bag batchwisely. It further discloses an operation of slicing the porous cross-linked polymer. It also contains a description to the effect that polypropylene (PP) is a preferred material for the film because it is sparingly adhesive to the porous cross-linked polymer, inexpensive, and capable of being recycled.
Then, WO-A-97-37745 discloses a method for producing a porous cross-linked polymer by coating the HIPE on the surface of a porous substrate (such as a felt), allowing at least a part of the HIPE to impregnate the porous substrate, and polymerizing the HIPE lodged in the substrate. It further discloses the necessity for polymerizing the HIPE as held in contact with such a polar material as PET, glass, or water for the purpose of endowing the porous cross-linked polymer with open cells.
Z. Bhumgara (Filtration and Separation, March, 1995, 245-251) describes the fact that in a copolymer of styrene and divinylbenzene, a porous cross-linked polymer with open cells is obtained by using PET, nylon 66, glass, or steel.
The method for polymerizing the HIPE which is disclosed in the official gazette of WO-A-97-27240, however, has the possibility of suffering the bag packed with the HIPE to acquire a larger thickness in the lower part thereof after the elapse of time from the packing operation and yet allowing the uniformity of thickness thereof to be upped to a certain extent by the subsequent reeling operation. Since the product of this method tends to give an increased thickness to the lower part thereof because of the weight of the HIPE itself and, worse still, tends to induce vertical deviation and separation of the oil phase and the liquid phase, it entails problems such as imposing limits on height (width) and thickness, rendering retention of uniformity of thickness, performance, and quality difficult, and permitting no free control of width and thickness. Further, since the operations ranging from packing the bag with the HIPE through polymerizing the packed HIPE cannot be continuously carried out and consequently the successive stages from the continuous step of packaging the bag with the HIPE through the batch step of polymerizing the HIPE in the bag constitute themselves rate-governing processes, the product has the problem of failing to make the most of the advantage of a continuous packing process. Further, since the method uses a bag made of film and, therefore, obtains exclusively a porous cross-linked polymer unique in terms of property, it entails the problem of failing to obtain a porous cross-linked polymer having different properties on the opposite surfaces thereof.
Though the official gazette of WO-A-97-37745 mentioned above has a description to the effect that the polymerization may be carried out by a batch operation or a continuous operation, whichever may fit the occasion better, it has absolutely no specific suggestion as to a method for continuous production of a HIPE using jointly a porous substrate and a polar material.
It is, therefore, an object of this invention to provide a method for the production of a porous cross-linked polymer which allows the produced porous cross-linked polymer to acquire a controlled surface property, permits free control of the width and the thickness of the polymer to be produced, and enables the operations ranging from supplying the HIPE through polymerizing the HIPE to be carried out continuously.
Further, the invention disclosed in the official gazette of WO-97-27240 neither contemplates selecting a film in view of durability at elevated temperature nor takes into due consideration the property fit for cyclic use of the product. The films disclosed by the prior inventions mentioned above use materials of limited quality. Such prior inventions have absolutely no specific suggestion about selecting a film which is excellent in durability fit for polymerization at elevated temperature (such as resistance to heat, resistance to monomer, resistance to hydrolysis, and suitability for cyclic use) and capable of controlling the surface properties (smoothness, capability of forming a texture with open cells, resistance to preclude formation of pinholes, and property of forming voids) of the produced porous cross-linked polymer.
Further, Z. Bhumgara (Filtration and Separation, March, 1995, 245-251) describes that a copolymer of styrene and divinylbenzene, by using PET, nylon 66, glass, or steel, is enabled to produce a porous cross-linked polymer with open cells. The PET is caused as by calcium chloride contained as a constituent component in the HIPE to succumb readily to hydrolysis with an alkaline water-phase component and this trend of the PET is particularly conspicuous when the temperature of polymerization is high. The nylon has a high water absorbing property and shows a phenomenon of swelling and consequently inducing a dimensional variation. The glass is brittle and deficient in heat transfer. The steel forms rust.
The official gazette contains no mention of a material which forms open cells during the copolymerization of a monomer mixture containing an acrylic ester. Neither does it contain any mention of continuous sheet polymerization.
It is another object of this invention, therefore, to provide a method for the production of a porous cross-linked polymer which, by selecting a sheet material containing a film capable of controlling the surface property of a porous cross-linked polymer to be produced, is enabled to fit the sheet material containing the film for repeated use, promise a reduction in cost, and render the property characteristic.
Then, the official gazette of WO-A-97-27240 has absolutely no specific suggestion of a slice method which enables a process ranging from a step of supplying the HIPE through a step of polymerizing it to a step of slicing the polymerized HIPE to be carried out continuously.
It is yet another object of this invention, therefore, to provide a method for the production of a porous cross-linked polymer which enables a process ranging from a step of supplying the HIPE through a step of slicing the polymerized HIPE to be carried out continuously.
The present inventors, after pursuing a diligent study in search of a novel method for the production of a porous cross-linked polymer which allows a process ranging from a step of supplying the HIPE through a step of polymerizing the HIPE (and further slicing the polymerized HIPE) to be carried out continuously, have perfected this invention.
Specifically, when the present inventors tried a method for producing a porous cross-linked polymer by continuously carrying out a process ranging from a step of supplying the HIPE through a step of polymerizing it (and further slicing the polymerized HIPE), they found this method to entail many problems such as giving rise to a part not thoroughly hardened and suffered to remain in the form of soft cream (or yogurt) notwithstanding the process ranting from the step of supplying the HIPE through the step of polymerizing this HIPE was carried out continuously and the heat treatment was performed at the prescribed hardening temperature for the prescribed length of time and suffering the produced porous cross-linked polymer to sustain in the surface part thereof pinholes and voids resembling pockmarks because the polymer separated water when the HIPE used therein had a W/O ratio reaching a level of some tens to some hundreds or because the polymer, when hardened, emitted free water. Thus, the inventors having published the official gazette of WO-A-97-27240 probably continued such experiments to find that the numerous problems attendant on the method of combination continuous and batch polymerization as contemplated by the invention disclosed in WO-A-97-27240 could be solved by continuously performing the process ranging from the step of supplying the HIPE through the step of polymerizing it (and further slicing the polymerized HIPE) and nevertheless could not do anything more than developing the method of combination continuous and batch polymerization because they failed to solve the technical problems inherent in an attempt to perform continuously the process ranging from the step of supplying the HIPE through the step of polymerizing it (and further slicing the polymerized HIPE). The invention disclosed in the official gazette of WO-A-97-37745 mentioned above, similarly to the invention disclosed in the official gazette of WO-A-97-27240, probably could not offer any specific suggestion on a continuous process of manufacture of the HIPE because the technical problems inherent in an attempt to perform continuously the process ranging from the step of supplying the HIPE through the step of polymerizing it (and further slicing the polymerized HIPE) could not be solved.
In the circumstances, the present inventors were convinced that the method of performing continuously a process ranging from the step of supplying the HIPE through the step of polymerizing it (and further slicing the polymerized HIPE) which remained yet to be developed was the only way of solving the technical problems inherent in a method for combination continuous and batch polymerization and, based on this belief, continued a diligent study with a view to solving such new technical problems as might arise from continuing the process (till the step of slicing the polymer). This invention has been perfected as a result.
To be specific, the problems of this invention are accomplished by the following items (1)-(14).
(1) A method for the production of a porous cross-linked polymer by the polymerization of a water-in-oil type high internal phase emulsion, characterized by causing the outer surface part of said emulsion by means for decreasing an oxygen content to assume an atmosphere or a state having a lower oxygen content than an ambient air and performing continuously a process ranging from a step of supplying said emulsion through a step of polymerizing said emulsion.
(2) A method for the production of a porous cross-linked polymer according to (1) above, wherein said means for decreasing the oxygen content of the outer surface part of the emulsion comprises at least one member selected from the group consisting of:
(A) a means for decreasing an oxygen content by using a gas which represses or prevents the contact of the ambient air with said emulsion by replacing a part or whole of the ambient air contacting with the outer surface part of said emulsion with a gas having a lower oxygen content than the ambient air;
(B) a means for decreasing an oxygen content by using a liquid which represses or prevents the contact of the ambient air with said emulsion by forming a liquid layer or a liquid film on the outer surface part of said emulsion with a liquid exerting no influence on the polymerization; and
(C) a means for decreasing an oxygen content by using a solid which represses or prevents the contact of the ambient air with said emulsion by forming a solid layer on the outer surface part of said emulsion with a solid capable of decreasing or nullifying the oxygen-contacting content.
(3) A method according to (2) mentioned above, wherein the means for decreasing the oxygen content by using a gas as set forth in (A) above is means for preventing the contact of the ambient air with the HIPE by having nitrogen gas replace the whole ambient air contacting the outer surface part of the emulsion.
(4) A method according to (2) or (3) mentioned above, wherein the means for decreasing the oxygen content by using a liquid as set forth in (B) above is means for preventing the contact of the ambient air with the emulsion by having an aqueous solution incapable of affecting polymerization form a water layer on the outer surface part of the emulsion.
(5) A method according to any of (2)-(4) mentioned above, wherein the means for decreasing the oxygen content by using a solid as set forth in (C) above is means for repressing or preventing the contact of the ambient air with the emulsion by having a sheet form a sheet layer on the outer surface part of the emulsion.
(6) A method according to (2) above, wherein the means for decreasing the oxygen content of the outer surface part of the emulsion is formed by combining means for preventing the contact of the ambient air with the emulsion by having nitrogen gas replace the whole of the ambient air contacting the outer surface part of the emulsion and means for repressing or preventing the contact of the ambient air with the emulsion by having a sheet form a sheet layer on the outer surface part of the emulsion.
(7) A method according to (2) above, wherein the means for decreasing the oxygen content of the outer surface part of the emulsion is formed by combining means for preventing the contact of the ambient air with the emulsion by having an aqueous solution incapable of affecting polymerization form a water layer on the outer surface part of the emulsion and means for repressing or preventing the contact of the ambient air with the emulsion by having a sheet form a sheet layer on the outer surface part of the emulsion.
(8) A method according to (2) above, wherein the means for decreasing the oxygen content of the outer surface part of the emulsion is formed by comprising means for repressing or preventing the contact of the ambient air with the emulsion by having a sheet form a sheet layer on the outer surface part of the emulsion.
(9) A method according to (2) above, wherein the gas permeability of said sheet layer formed on the outer surface part of said emulsion as the means for decreasing an oxygen content by using a sheet set forth in said means (C) is not more than 100 cm3/cm2xc2x7s.
(10) A method according to any of (1)-(9) above, wherein the sheet set forth in (C) above to be used as the sheet layer formed on the outer surface part of the emulsion as means for decreasing the oxygen content is one member or a combination of two or more members selected from the group consisting of {circle around (1)} at least one sheet material selected from the group consisting of a film, a non-woven fabric and a woven fabric, {circle around (2)} an endless belt and/or a band-shaped plate made of a metal and/or a resin, {circle around (3)} an endless belt and/or a band-shaped plate made of a metal and using said sheet material on the surface thereof destined to contact with the outer surface part of said emulsion, and {circle around (4)} an endless belt and/or a band-shaped plate made of a resin and using said sheet material on the surface thereof destined to contact with the outer surface part of said emulsion.
(11) A method according to any one of (2)-(10) above, wherein said sheet is formed of at least one material selected from the group (I) consisting of a fluorine resin, a silicone resin, heat-resistant resins, thermoplastic polyester resins, and thermoplastic polyester type elastomer resins, and/or is coated with at least one material selected from said group (I).
(12) A method according to any one of claims (2)-(11) above, wherein said sheet is formed of at least one material selected from the group (II) consisting of a fluorine resin, a silicone resin, polyimide, polyphenylene sulfide, polysulfone, polyether sulfone, polyether imide, polyether ether ketone, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polycyclohexane terephthalate, and stainless steel or is coated with at least one material selected from said group (II).
(13) A method according to any of (1)-(12) above, wherein a process ranging from a step of supplying the emulsion through a step of polymerizing the emulsion is continuously carried out in a horizontal line.
(14) A method according to any one of (2)-(13) above, wherein said means for decreasing an oxygen content by using a sheet set forth in said means (C) is characterized by the facts that:
(1) said sheet to be used on the outer surface part of said emulsion is one member or a combination of two or more members selected from the group consisting of {circle around (1)} endless belts and {circle around (2)} endless belts made of a metal or a resin and using said sheet material on the surface thereof contacting with the outer surface part of said emulsion and
(2) said endless belt has the temperature thereof adjusted with a hot water shower:
(15) A method according to any of (1)-(14) above, which further comprises a step of continuously slicing a porous cross-linked polymer obtained by polymerization.
The present inventors have further discovered a novel material which is free from the defects found in the porous cross-linked polymer with open cells proposed by Z. Bhumgara (Filtration and Separation, March 1995, 245-251) and the official gazette of WO-A-97-27240 (Shell Oil Company) and capable of imparting open cells to the surf ace of a porous cross-linked polymer obtained by polymerizing HIPE. Specifically, they have found that fluorine resins such as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-perfluoroalkylvinyl ethers, silicone resins such as dimethyl polysiloxane, dimethyl siloxane-diphenyl siloxane copolymer, and thermosetting silicone resin, heat-resistant resins such as polyimide, polyphenylene sulfide, polysulfone, polyether sulfone, polyether imide, and polyether ether ketone, antihydrolytic polyesters such as polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polycyclohexane terephthalate, and polycyclohexane terephthalate, and stainless steel are materials which can accomplish the objects of this invention. They have further acquired a knowledge that these materials abound in resistance to heat, resistance to hydrolysis, resistance to water, toughness, and resistance to corrosion, impose sparing restrictions on the composition of HIPE and the conditions of polymerization, and prove suitable as materials for an apparatus for polymerization. This invention has been perfected on the basis of this knowledge.
Specifically, still another object of this invention consists in providing (16) a method for the production of a porous cross-linking agent formed by polymerizing HIPE and possessed of open cells, which method is characterized by the fact that the part of an apparatus for polymerization destined to contact the HIPE is formed of at least one material selected from the group consisting of fluorine resin, silicone resin; polyimide, polyphenylene sulfide, polysulfones, polyether sulfone, polyether imide, polyether ether ketone; polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polysiloxane terephthalate; and stainless steel and/or is coated with at least one of these materials.
Yet another object of this invention consists in providing (17) a method for the production of a porous cross-linked polymer set forth in (16) above, wherein the monomer composition contained in the HIPE mentioned above contains as an essential component a (meth)acrylic ester.